The objective is to gain knowledge of the genetics and physiology of poliovirus. Two specific areas will receive primary attention: viral RNA synthesis and viral genetics. The study of RNA metabolism will focus on the recent evidence that the host-factor needed to allow initiation of minus strand synthesis by the viral polymerase may be terminal uridyl transferase (TUT). The association of host-factor with TUT will be examined critically, primarily through the generation of monoclonal antibodies. The possibility will be examined that viral RNA synthesis involves first the formation of a hairpin, and then its cleavage leaving VPg at the 5'-end. Viral genetic studies will concentrate on the use of an infectious polio cDNA clone to generate and study defined mutants. Five good mutants have already been generated using three insertion or deletion methods and more mutants will be sought using the same methods. Complementation and recombination among the mutants will be studied. Inertypic recombinants will be examined to determine what sequences are involved in recombination. The phenotypes of the mutants will be examined to link individual proteins to specific functions and to understand the range of functions involved in poliovirus growth. Because poliovirus is a prototype of all picornaviruses, these studies will be applicable to many viral systems.